FIG. 1 is a schematic diagram of the structure of a cellular wireless communication system in prior art. As shown in FIG. 1, the cellular wireless communication system mainly includes: a terminal (User Equipment, referred to as UE), an access network and a core network, wherein the terminal refers to various equipments which can communicate with the cellular wireless communication network, such as, mobile phone or notebook PC. The Radio Access Network (RAN) refers to the network composed of a base station, or the network composed of a base station and a base station controller, and is mainly responsible for access stratum service, such as radio resource management. There is a physical connection or a logical connection between the base stations according to actual situations, such as, the connection between the base station 1 and the base station 2, and the connection between the base station 1 and the base station 3 shown in FIG. 1. The core network is an anchor point of the user plane, and is mainly responsible for non-access stratum service, such as location update. Each of the base stations can connect one or more core network (CN) nodes.
In the cellular wireless communication system, the wireless coverage of a fixed base station network will be restricted due to some reasons, such as, the blocking that building structure creates for radio signal caused will result in a coverage loophole for the wireless network. In addition, at the cell edge area, due to the weakening of wireless signal intensity in the edge area of the cell and the interference of neighboring cells, the communication quality of the UE at the cell edge area will be poorer, and error rate of wireless transmission will increase. In order to improve the coverage rate of the data rate, group mobility, temporary network deployment, throughput at the cell edge area, and coverage of a new area, a wireless network node, which is referred to as relay node/relay station, is introduced in the cellular wireless communication system.
The relay node (referred to as Relay below) has the function of relaying data and possible control information via a wireless link. FIG. 2 is a schematic diagram of a network architecture including the relay in prior art. As shown in FIG. 2, the UE directly served by a base station (eNodeB, which can also be abbreviated to eNB) is referred to as a Macro UE, and the UE served by the Relay is referred to as Relay UE, wherein a direct link refers to the wireless link between the base station and the UE, which includes an uplink/downlink (UL/DL) direct link; an access link refers to the wireless link between the Relay and the UE, which includes a DL/UL access link; and a backhaul link refers to the wireless link between the base station and the Relay, which includes a DL/UL relay link.
There are many ways for the Relay to relay data, for example, amplifying directly the wireless signal received from a base station; or forwarding the correctly received data packet to the terminal after performing a corresponding process on the received data sent from the base station; or sending data to the terminal by the base station cooperating with the Relay, and also the Relay being used for relaying the data sent from the terminal to the base station.
In the above, there is a relay, which has the following characteristics:
the UE can not distinguish the relay from the cell of the fixed base station, that is to say, from the viewpoint of the UE, the relay itself is a cell which has no difference from the cell of the fixed base station, and such cell can be referred to as a relay cell. The relay cell has its own physical cell identity (PCI), which can send broadcast, similar to a common cell. When the UE resides in the relay cell, the relay cell can allocate and schedule radio resource to the UE separately, which can be independent of the radio resource scheduling for the base station engaging in relaying (the base station is referred to as a Donor base station, that is, the base station connected with the Relay via a backhaul link). Interface and protocol stack between the relay cell and the UE are identical with those between a common base station cell and a UE.
FIG. 3 is a schematic diagram of flat structure of in related art. As shown in FIG. 3, the IP (Internet Protocol)-based long term evolution (LTE) system consists of an E-UTRAN (Evolved Universal Terrestrial Radio Access Network), a CN node, and other support nodes, wherein the CN node includes a MME (Mobility Management Entity) and a S-GW (Serving Gateway), wherein the MME is responsible for control plane related tasks, such as mobility management, signaling processing in non-access stratum, and context management of mobility management for the UE; the S-GW is responsible for data transferring, retransmitting, and routing switching for the UE plane; the eNBs interconnect with each other via X2 interface in logic to support the mobility of the UE in the whole network, so as to ensure seamless switching of the UE; each eNB is connected to a SAE (System Architecture Evolution) core network via S1 interface, that is to say, connected to MME via the control plane S1-MME interface, connected to the S-GW via the S1-U interface of user plane, wherein the S1 interface supports multipoint connection between the eNB and the MME and between the eNB and the S-GW.
FIG. 4 is a schematic diagram of protocol stack of S1-MME interface in related art. As shown in FIG. 4, the network layer of S1-MME interface employs IP protocol, the transport layer above the network layer employs the SCTP protocol, and the application layer in uppermost layer (that is S1-AP protocol of the control plane) employs the S1-AP signaling transmitted by the transmission bearer in bottom layer, and the layers below the network layer which employs IP-based S1-MME interface sequentially are the data link layer and the physical layer. FIG. 5 is a schematic diagram of protocol stack of S1-U interface in related art. As shown in FIG. 5, the User plane of GPRS (General Packet Radio Service) Tunneling Protocol (GTP-U)/User Datagram Protocol (UDP)/IP constitute transmission bearer for transmitting the user plane PDU (Protocol Data Unit) between the eNB and the S-GW. The transmission bearer is identified by tunnel endpoint identifiers (TEID) of the GTP-U including the source side GTP-U TEID and the target side GTP-U TEID, and IP addresses including the source side IP address and the target side IP address, wherein the UDP port number is fixed as 2152; the GTP-U is a tunneling protocol for implementing the seamless transmission on the IPv4 and the IPv6. Each transmission bearer is used to carry service data flows.
Each eNB performs the signaling and data transmission with the UE via a Uu interface (which is defined as the wireless interface between the UTRAN and the UE initially). FIG. 6 and FIG. 7 illustrate protocol stack of the air interface between the eNB and L1, L2, L3 of the UE respectively from the control plane and the UE plane.
FIG. 8 is a schematic diagram of the bearer structure of the LTE system in related art. As shown in FIG. 8, the LTE system can provide end-to-end service, and ensure quality of service (QoS) of the provided service through the parameters carried particularly. The granularity ensured by the QoS level of the bearers of the Evolved Packet Core (EPC) and the E-UTRAN is EPS bearer/E-RAB (E-UTRAN Radio Access Bearer). Data packet carried by the EPS bearer is transmitted between the S-GW and PDN gateway (P-GW) via S5/S8 bearer. The data packet of the E-RAB is transmitted between the eNodeB and the S-GW via S1 Bearer, and transmitted between the UE and the eNodeB via radio bearer (RB).
For the LTE system in which the relay cell is introduced, there is still no technical solution for the Relay node to relay data between the UE and the S-GW.